In the field of blood coagulation, it is known to determine the parameters known as Activated Partial Thromboplastin Time (APTT) and/or the Prothrombin Time (PT). Both parameters give a value indicating the time required for blood coagulation. In principle, these measures do not require any specialized personnel or special equipment and they can be determined in hospitals or non-specialized laboratories. Moreover, particular devices exist, even Point of Care (POC) devices for determining these parameters in the hospitals or at home.
Examples of these devices include the CoaguCheck Plus® (CCP®) commercially available from e.g. Boehringer Mannheim. It is a battery powered, portable laser photometer with APTT reagents (for intrinsic pathway coagulation) and PT reagents (for extrinsic pathway coagulation). The reagents are disposed in a wafer-like disposable plastic reagent cartridge/strip. A sample of whole blood is applied to an application well in the cartridge and blood flows through capillary action to the reagent chamber.
Coagulation starts when the blood of the sample comes into contact with the reagents and is considered to have stopped when the photometer detects cessation of blood flow. The detection is based on sensing the variation in light scatter from red cells. The time between blood application and blood clotting is measured and converted to the plasma equivalents APTT or PT.
The document WO9013034 discloses a test strip comprising an orifice or area adapted to receive a sample of whole blood, a capillary track leading the sample to a zone comprising the reagents for initiating coagulation and for the in situ measure of APTT. The strip is also provided with a venting port. The aim of the device is the determination of blood flow stoppage independently of the blood haematocrit, which has been reported as an inconvenient in test strips using blood samples as fluid test.
Determination of APTT or PT, as well as of other blood parameters, is of great relevance for patients receiving anti-coagulant treatments. In the same way, coagulation time is a critical aspect in intensive care units for the monitoring of heparin treatment and in preoperative assessment of blood coagulation. As a general rule, APTT or PT may be easily determined in normal conditions, which means that the subject (patient) does not have any inherited or acquired coagulation factor deficiency. APTT and/or PT may be altered when the subject has a coagulation factor deficiency, making further diagnostic tests necessary. In these scenarios patients are redirected to more specialized hospitals or analytical laboratories, which elongate the diagnosis time. This also supposes an uncomfortable procedure for the patient. Another disadvantage is that relatively high amount of blood (namely the further processed plasma) may be required.
The standardised mode to measure the deficiency of one or more coagulation factors can be summarized as follows. A plasma test sample is firstly diluted with a buffer, and then mixed with factor depleted-plasma which is deficient only in the coagulation factor that is going to be detected in the test sample, and comprising all other coagulation factors. Next, reagents either from the extrinsic or intrinsic coagulation pathway needed to start coagulation are added to the mixture. Coagulation is then only dependent on the limiting coagulation factor, corresponding to the one being measured in the test sample. A modification of this standardised method is in particular disclosed for factor V activity in the document WO9720066. The document WO9720066 discloses the way for determining if a patient is susceptible of suffering a thromboembolism. Analysis is performed using plasma and determining the ratio between factor V activity level without activated protein C (APC) and the factor V activity level with APC. Factor V depleted plasma is added to increase the specificity of the test.
Among the commercial tests adapted for detecting coagulation factor deficiencies, the test known as Actin FS® from Baxter Diagnostics Inc. is one of the multiple examples commonly used in the specialized laboratories to test coagulation factor activities in plasma samples. The test includes all the reagents for an APTT determination (purified soy phosphatides, ellagic acid activator and calcium) in liquid form and ready for use. It allows analysing factor defects of factors VIII, IX, XI, and XII with high sensitivity and specificity.
As above exposed all these test are performed on plasma and require venous blood samples.
It is an object of the present invention to provide methods and devices that at least partially solve one or more of the aforementioned problems.